(a) Technical Field
The present invention relates to a CMOS image sensor and a manufacturing method thereof.
(b) Description of Related Art
A semiconductor image sensor is a semiconductor device converting optical images into electrical signals and typically manufactured in a type of a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) image sensor.
A charge coupled device is an integrated circuit containing an array coupled capacitors. Each capacitor stores and transfers electric charges to one or more of the neighboring capacitors thereof.
In contrast, a CMOS image sensor includes MOS transistors, photo-sensing regions for detecting an external light and generating and accumulating photocharges upon receiving external light, and a logic circuit area for processing to convert the light into electric signals. A CMOS image sensor also includes color filters arranged over the photo-sensing region.
The photo-sensing region may have formed therein a photodiode. An incident light generates electron-hole pairs (EHP) in the photodiode, wherein the holes are absorbed into the semiconductor substrate and the electrons are accumulated at the photodiode. In order to improve characteristics of the CMOS image sensor, it is important to hold the electrons without loss and transfer potential variation of the photodiode to a gate electrode of an adjacent MOS transistor without loss.
A conventional CMOS image sensor may be described with reference to FIGS. 7 and 8, wherein FIG. 7 is a plan view of a conventional CMOS image sensor 100, and FIG. 8 is a cross-sectional view of CMOS image sensor 100 along line I-I′ of FIG. 7. As shown in FIGS. 7 and 8, CMOS image sensor 100 is formed on a semiconductor substrate 102 and includes an active device 104 and a photodiode 106. A device isolation region 108 isolates device 104 from other devices (not shown) of CMOS image sensor 100. A gate terminal 110 is provided over active device 104. An insulating layer 112 is provided over gate terminal 110 and photodiode 106 and two contact holes 114 and 116 are respectively formed in insulating layer 112 over gate terminal 110 and photodiode 106. Metal plugs 118 and 120 are filled in contact holes 114 and 116, respectively. A connecting member 122 is deposited over the structure and is connected to both metal plugs 118 and 120. Metal plugs 118 and 120 may comprise tungsten and connecting member 122 may comprise aluminum. Thus, photodiode 106 is connected to gate terminal 110 through metal plug 120, connecting member 122, and metal plug 118, and the connection between photodiode 106 and gate terminal 110 includes four joints.
Conventional CMOS image sensors such as CMOS image sensor 100 have a drawback in that photodiode 106 may be damaged when contact hole 116 is formed by a dry etching technique. Furthermore, because photodiode 106 and gate terminal 110 are connected through four contact joints, the potential of photodiode 106 is transferred to the gate terminal 110 with loss, thus degrading the characteristics of CMOS image sensor 100.